The WikiLeaks founder Julian Assange was made an Ecuadorian citizen last month, the nation’s foreign ministry has revealed, in an attempt to resolve the political impasse over his continued presence in the UK.

The 46-year-old has been naturalised after living for five and a half years in the cramped, Latin American country’s embassy in Knightsbridge, central London.

Earlier this week the UK’s Foreign Office revealed that Ecuador had asked for Assange, who was born in Australia, to be accredited as a diplomat. The request was dismissed.

The Ecuadorian initiative was intended to confer legal immunity on Assange, allowing him to slip out of the embassy and Britain without being arrested for breaching his former bail conditions.

Julian Assange posted this picture of himself in an Ecuadorian football shirt on Twitter. Photograph: Twitter

Assange failed to surrender to the UK authorities in 2012 after the supreme court rejected his appeal against extradition to Sweden to face accusations of sexual crimes, including rape. He was granted asylum in the Ecuadorian embassy.

Swedish prosecutors last year unexpectedly dropped their investigation into allegations against him, which he denied. WikiLeaks, however, fears that the US will seek his extradition if he leaves the embassy, believing there is a sealed US indictment seeking his arrest.

At a press conference on Thursday in the Ecuadorian capital, Quito, the foreign minister, María Fernanda Espinosa, explained that Assange had sought citizenship and that it had been granted on 12 December last year.

“The Ecuadorian government is empowered to grant nationality to the protected person and thus facilitate ... his inclusion in the host state,” Espinosa told reporters.

Assange’s life could be under threat from other states, she warned, adding that she was seeking a “dignified and just” solution to his situation with Britain.

On Wednesday evening, the UK Foreign Office put out a statement explaining that: “The government of Ecuador recently requested diplomatic status for Mr Assange here in the UK. The UK did not grant that request, nor are we in talks with Ecuador on this matter. Ecuador knows that the way to resolve this issue is for Julian Assange to leave the embassy to face justice.”

At the same time Assange appeared on his Twitter account for the first time wearing an Ecuadorian national football shirt.

A statement by Assange’s legal team said: “The UN ruling, issued almost two years ago, is crystal clear in its language. [He] is unlawfully and arbitrarily detained by the UK authorities and must be released. The UK should not permit itself to be intimidated by the Trump administration’s public threats to ‘take down’ Mr Assange.”